A spark plug used for an internal combustion engine or a similar engine includes, for example, an insulator, a center electrode, a tubular metal shell, and a rod-shaped ground electrode. The insulator has an axial hole extending along a direction of an axial line. The center electrode is disposed to be inserted in a front end side of the axial hole. The metal shell is disposed on an outer periphery of the insulator. The ground electrode is secured to the front end portion of the metal shell. Also, a spark discharge gap is formed between a front end portion of the ground electrode and a front end portion of the center electrode. When a voltage is applied to the spark discharge gap, a spark discharge is generated.
In addition, in a known technique for enhancing the ignitability and durability, a chip made of a noble metal alloy or a similar alloy is disposed at the front end portion of the ground electrode. The gap is formed between the chip and the center electrode. Furthermore, a technique is proposed for further enhancing the ignitability (for example, see WO 2009/066714). In this technique, a chip is bonded to the front end surface of the ground electrode and projects from the front end surface. This allows reducing flame quenching by the ground electrode.